Swine manure application enriches the soil food web in corn and soybean production.

Strategies for managing plant-parasitic nematodes while promoting soil quality are needed in corn (Zea mays) and soybean (Glycine max) cropping systems. Therefore, a series of two-year experiments were conducted in Minnesota to determine the simple and interactive effects of manure or conventional fertilizer and short-term crop rotation on the nematode community, a sensitive indicator of soil ecology. The two-year crop sequences were Sus-Sus, Res-Sus, and Corn-Sus, where Sus and Res are soybean susceptible and resistant to Heterodera glycines (soybean cyst nematode: SCN), respectively. The fertilizer treatments were liquid swine manure, conventional phosphorus (P)-potassium (K) fertilizer, and no fertilizer. Crop sequence and fertilizer choice had individual main effects, but did not have an interactive effect on the nematode community. Swine manure affected the nematode community in ways that conventional PK fertilizer or no fertilizer did not, substantially enhancing populations of bacterivores in colonizer-persister group 1, which are extreme enrichment opportunists. Manure application did not affect other groups of free-living nematodes and decreased nematode community diversity. Conventional PK fertilizer did not influence the nematode community compared with untreated control. The effects of short-term crop sequences were much less pronounced and consistent than manure application, but corn altered the environment to favor fungivores while soybean increased bacterivore abundances.Strategies for managing plant-parasitic nematodes while promoting soil quality are needed in corn (Zea mays) and soybean (Glycine max) cropping systems. Therefore, a series of two-year experiments were conducted in Minnesota to determine the simple and interactive effects of manure or conventional fertilizer and short-term crop rotation on the nematode community, a sensitive indicator of soil ecology. The two-year crop sequences were Sus-Sus, Res-Sus, and Corn-Sus, where Sus and Res are soybean susceptible and resistant to Heterodera glycines (soybean cyst nematode: SCN), respectively. The fertilizer treatments were liquid swine manure, conventional phosphorus (P)-potassium (K) fertilizer, and no fertilizer. Crop sequence and fertilizer choice had individual main effects, but did not have an interactive effect on the nematode community. Swine manure affected the nematode community in ways that conventional PK fertilizer or no fertilizer did not, substantially enhancing populations of bacterivores in colonizer-persister group 1, which are extreme enrichment opportunists. Manure application did not affect other groups of free-living nematodes and decreased nematode community diversity. Conventional PK fertilizer did not influence the nematode community compared with untreated control. The effects of short-term crop sequences were much less pronounced and consistent than manure application, but corn altered the environment to favor fungivores while soybean increased bacterivore abundances.

Drainage and Nitrate Leaching from Artificially Drained Maize Fields Simulated by the Precision Nitrogen Management Model.

Environmental nitrogen (N) losses (e.g., nitrate leaching, denitrification, and ammonia volatilization) frequently occur in maize ( L.) agroecosystems. Decision support systems, designed to optimize the application of N fertilizer in these systems, have been developed using physically based models such as the Precision Nitrogen Management (PNM) model of soil and crop processes, which is an integral component of Adapt-N, a decision support tool providing N fertilizer recommendations for maize production. Such models can also be used to estimate N losses associated with particular management practices and over a range of current climates and future climate projections. The objectives of this study were to update the PNM model to include an option for simulating soil-water processes in artificially drained soils, and to calibrate the revised PNM model and test it against multiyear field studies in New York and Minnesota with different soils and management practices. Minimal calibration was required for the model. Denitrification rate constants were calibrated by minimizing the error between simulated and observed nitrate leaching for each study site. The normalized root mean squared error of cumulative daily drainage for the validation sets ranged from 10 to 23%. For cumulative daily nitrate leaching, the normalized root mean squared error ranged from 11 to 28% for the validation sets. The minimal calibration required and relatively simple data inputs make the PNM model a broadly applicable tool for simulating water and N flows in maize systems.

Predicting nitrate-nitrogen loads in subsurface drainage as a function of fertilizer application rate and timing in southern Minnesota.

Fertilizer management practices that focus on applying N fertilizer at the right rate and time have been proposed as a practical option to reduce NO3 -N losses from subsurface drained agricultural fields. In this study, regression equations were developed to predict NO3 -N losses for a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation in southern Minnesota, using fertilizer application timing and rate and growing season precipitation as inputs. The equations were developed using the results of the field-scale hydrologic and N simulation model DRAINMOD-NII, first calibrated and validated for three sites in southern Minnesota, and then run with different combinations of N fertilizer application rates and timings. Fertilizer timing treatments included a single application in the fall or spring and a split-spring application (half applied preplant and the remaining applied as sidedress). The predictive regression equations showed that the split fertilizer application timing could reduce regional N loads by 28% compared with spring or fall applications. Greater reductions were predicted when the split timing was combined with lower N fertilizer rates. Utilizing the split application timing and reducing the fertilizer rate by 10 and 30% showed 33 and 41% reductions in N loads, respectively, compared with current fertilizer management practices. Such reductions in fertilizer application rates could be achieved through the use of variable-rate nitrogen (VRN) fertilizer technologies. Results of this modeling study indicate that synchronizing fertilizer application with crop requirements and utilizing VRN technologies could significantly reduce N loads to surface waters in southern Minnesota.

Nitrate Loss in Subsurface Drainage from a Corn-Soybean Rotation as Affected by Nitrogen Rate and Nitrapyrin.

Successful N management practices for the US Midwest must optimize crop production and minimize NO-N losses from subsurface tile drainage. The objective of this study was to measure the effects of N rate, N application timing, and nitrapyrin [2-chloro-6-(trichlormethyl) pyridine] on corn ( L.) production and NO-N in tile drainage water in a corn-soybean [ (L.) Merr.] rotation in Minnesota. Anhydrous ammonia was applied at 90 and 179 kg ha with nitrapyrin in the fall and at 134 kg ha with and without nitrapyrin in fall and spring. However, drainage water monitoring was only conducted on fall treatments. Over a 5-yr period, 71% of drainage occurred in April through June and <1% occurred from November through March due to frozen soil. Averaged across N treatments and crops, annual drainage ranged from 69 to 380 mm among years. From 2001 through 2003, NO-N concentrations averaged 13.8, 15.6, and 20.0 mg L in corn and 7.3, 8.2, and 12.6 mg L in soybean when 90, 134, and 179 kg N ha was fall applied with nitrapyrin to corn, respectively. Corn grain yields were greater with spring-applied N at 134 kg ha (11.3 Mg ha) than with fall-applied N at 134 and 179 kg ha with nitrapyrin (10.5 and 10.8 Mg ha, respectively), and nitrapyrin did not affect corn production or water quality. Fall application of N is common on cold soils in Minnesota. These data showed that fall application required a greater rate of N to optimize yield than spring and that greater fall rate often increased NO-N concentration and load in tile drainage water.